The use of silver halide technology in the Graphics Arts Industry has been primarily focused on the creation of high contrast systems, which are necessary to obtain strong image discrimination and good image quality/dot characteristics. The earliest high contrast system, called the "lith" system, used a low sulfite, hydroquinone based developer with silver chlorobromide emulsions, further modified by polyethylene oxide compounds.
Although the lith system provides high contrast, excellent image discrimination and good "dot" characteristics, the developer is unstable. The system requires a multi-part, compound developer and a low temperature (75-80.degree. F.) processing solution in order to maintain controlled developing conditions. These conditions require long processing times, sometimes as much as 2 minutes for development, but more commonly 1 minute. The process is further complicated by the fact that non-lith films are frequently processed in the same developers due to convenient configurations at various customers.
To increase development rates and reduce processing times, the Graphics Arts Industry gravitated toward the use of auxiliary developing agents in addition to hydroquinone. These agents include metol, phenidone, and the like. To increase developer life, the developing solutions employed higher concentrations of sulfite, which also increased their resistance to air oxidation, afforded greater uniformity of developer condition, and increased the development rate by allowing an increase in the temperature of the processing solution. These new "rapid access" developers were simpler to maintain and required about 30 seconds of development time, affording faster throughput, ease of operation, and greater compatibility with non-lith type films. The greatest drawback of these systems is the lack of the excellent image discrimination and dot characteristics achieved with the lith system.
U.S. Pat. No. 3,730,727 describes the use of formyl phenylhydrazines in the developer to improve image discrimination without the use of the low-sulfite lith techniques. U.S. Pat. No. 4,224,401 describes a lith-type result with a high pH, high sulfite-type developer solution. In U.S. Pat. No. 4,269,929, the system was further refined by the use of alkanol amines to lower the operable pH of the developer to practical levels, thus permitting commercialization of the type of developer known as "hybrid" developer. Hybrid developers provide the results of lith developers but at rapid access developing speeds.
Subsequently, U.S. Pat. Nos. 4,686,167, 4,798,780, 4,937,160, and 4,882,261, all teach novel hydrazine nucleators that afford the hybrid effect. Although hybrid systems have been commercialized, the alkanol amines used to boost or promote high contrast, require a pH of 11.0 or greater. This high pH has an adverse effect on the process equipment and is incompatible with the great variety of non-hybrid lithographic films that are frequently processed in the same chemistries.
U.S. Pat. Nos. 4,975,354 and 4,994,365 describe a new hybrid system that removes the alkanol amines from the developer and positions them in the film. These amines, ostensibly called boosters, activate the film incorporating the hydrazine nucleators, making them compatible with standard, low cost developing solutions.
The drawback of systems that incorporate alkanol amine boosters into the film containing the nucleators is the complexity of balancing the nucleator with the boosters to provide good discrimination at low fog or pepper levels while broadening the degree of compatibility with a number of existing rapid access developer systems. U.S. Pat. No. 5,264,323 describes the complications of balancing the hybrid systems which involves both nucleator and booster.
U.S. Pat. No. 4,994,365 describes the use of alkyl-ballasted quaternary pyridine nucleators, compatible with the boosters, which afford good discrimination and dot quality. However, interaction between the nucleator and booster makes the system incompatible with many rapid access systems.
U.S. Pat. No. 4,975,354 first described the use of "booster" technology, and U.S. Pat. No. 4,994,365 describes the use of alkyl ballasted pyridine nucleators as a method to improve image quality with the incorporated boosters.
U.S. Pat. No. 5,451,486, incorporated herein by reference, describes aryl sulfonamidophenyl hydrazides having alkenyl pyridinium functionality that offers improved performance as contrast enhancing nucleators.
U.S. Pat. No. 5,439,776, incorporated herein by reference, describes isothiouronium salts that serve as photographic nucleating agents and advances the use of substituted hydrazines as contrast enhancing nucleators.
Thus, a need exists for nucleator compounds having contrast enhancing properties superior to those previously disclosed along with high dot quality and film speed.